1. Field of the Invention
The present invention concerns a method to create x-ray images using two different energy spectra (“dual energy”), known as dual energy x-ray images, as well as an x-ray system designed to create dual energy x-ray images.
2. Description of the Prior Art
U.S. Pat. No. 6,683,934 B1 describes a method to create dual energy x-ray images in mammography, wherein an x-ray filter made of copper (Cu) that is 0.25 mm thick is used for the high-energy images and an x-ray filter made of aluminum (Al) that is 2 mm thick is used for the low-energy images.
US 2005/0243970 A1 describes an x-ray system for use in mammography. A special x-ray filter is used in order to reduce a radiation exposure of the patient.
In order to be able to better show a tumor or a lesion in an x-ray image, it is known to inject a contrast agent (iodine, for example) into a patient to be examined. Particularly, in the case of malignant tumors, an enrichment of the contrast agent in the tumor takes place due to the neovascularization. For presentation, according to the prior art a dual energy imaging is used, wherein a low-energy image (x-ray voltage in a range from 20 to 35 kVp) and a high-energy image (x-ray voltage in a range from 40 to 50 kVp) are created from the same volume segment. The low-energy image (in which the contrast agent is not perceptible, or is nearly imperceptible) is subsequently subtracted from the high-energy image (in which the contrast agent is better visible).
Dual energy imaging, also known as the two spectra method, is used in mammography in order to achieve an improved diagnosis for the radiologist as well as an improvement of the sensitivity and specificity. An x-ray system to create dual energy x-ray images must satisfy the following conditions as well as possible, in particular in the creation of the high-energy images:                An optimal quantum yield should be achieved.        The high-energy images should exhibit an optimally high contrast-to-noise ratio.        The x-ray dose used to create the high-energy images should be as low as possible.        